Pigments are incorporated in compositions such as paints and inks for giving color thereto. This is a very painstaking task because of poor the dispesibility of pigments. In order to disperse a pigment in a composition, such as a paint, it is a conventional practice to prepare a so-called pigment paste first by premixing a small amount of resin throughly with the pigment and then dilute the same with a specified resin and a solvent into a paint or ink composition. It is necessary that the resin must have a very high degree of affinity to pigments and no activity which is detrimental to the properties of the target paint and other compositions.
Now, it is generally understood that most pigments have an acidic, basic, or amphoteric capacity, and it has been reported that improved dispersibility could be obtained by intoroducing a group having a capacity contrary to such capacity of a pigment into a resin. For example, it has been proposed to introduce into the resin an acidic group or a basic group, or both of them, in order to improve its affinity to the pigment. From the angle of resin configuration, there has been proposed a star-form resin having chains extending radially from the center as produced by a polymerization reaction of a central material having several active points which act as starting points of the reaction. This star-form resin makes it easy to obtain a pigment paste of low viscosity, because the resin itself is of low viscosity. In addition, attempts have been made to further improve the capabilities of this star-form resin by incorporating an acidic group and/or a basic group therein.
However, none of the above mentioned methods have been fully successful and further property improvement of the properties is demanded.
The present inventors have found that a modified aluminum chelate resin produced by reacting an aluminum chelate with a resin having an active hydrogen bonded to an electrophilic atom or atomic group and/or an epoxy group has excellent pigment dispersibility, and that a paint prepared using the resin had various high-value capabilities. The modified aluminum chelate resin showed good dispersibility in relation to a wide range of pigments, whether acidic or basic, or amphoteric, and good improvement was found with pigment pastes thus obtained in respect to coloring power, gloss and fluidity.
It may be noted that in order to improve the dispersibility of pigments, several methods are known which are directed to chemically treating the surface of pigment particles, including, for example, methods for treating the particles with aluminum chelate (Japanese Patent Publication (unexamined) No. 125475/1981 and 195163/1975), and a method for treating with a titanium compound (Japanese Patent Publication (unexamined) No. 145448/1975). In these methods, however, it is necessary that the pigment and such metallic compound be thoroughly mixed in a mortar before the pigment is dispersed, which is quite laborious work.
The present invention, as above stated, is such that a specific resin is modified with aluminum chelate, and therefore it is clearly different which a pigment is treated with an aluminum chelate.
Hitherto, it has been known that a coating composition containing an aluminum chelate compound therein is liable to cause gelation of the resin component present therein during storage. When causing such specific resin as above mentioned to react with an aluminum chelate compound was, some anxiety about progress of gelation. In fact, however, there was no progress of gelation and the reaction of the specific resin with the aluminum chelate compound progressed smoothly.